Non-sweating doctor blade support



1965 A. E. KEYWORTH, JR 3,221,357

NON-SWEATING DOCTOR BLADE SUPPORT Filed Nov. 1, 1962 United States Patent Ofilice 3,221,357 Patented Dec. 7, 1965 3,221,357 NON-SWEATING DOCTOR BLADE SUPPORT Arthur E. Ke-yworth, Jr., East Walpole, Mass, assignor to Bird Machine Company, South Walpole, Mass, a corporation of Massachusetts Filed Nov. 1, 1962, Ser. No. 234,637 Claims. (Cl. -256.51)

This invention relates to a support for a doctor blade used in doctoring heated surfaces such as heated rolls in paper machines. More particularly it pertains to improvements in doctor blade supports whereby the edge of the blade may be positioned precisely and maintained in exact position with respect to the heated surface or roll against which it operates.

This application incorporates the disclosure in my copending United States patent application Serial No. 215,- 124, filed August 6, 1962 (now abandoned), and is in part a continuation thereof.

In paper machinery it is customary to use doctor blades in the form of relatively thin strips of metal in order to maintain clean surfaces on heated rolls or other moving surfaces over which the web of paper passes. Because the doctor blade itself is structurally weak and may extend for lengths of the order of feet from side to side of the paper machine, external supports are provided in order to prevent sagging or bending of the blade along its length under the influence of gravity. Such supports provide rigidity to the doctor blade and are formed to hold the doctor blade in a line completely straight and parallel with the surface of the heated roll. By control of the position of the blade support, uniform contact pressure may be maintained between the blade and the roll surface throughout the length of the blade. However, heat from the roll causes uneven heating and warping of the blade support, and various arrangements have been proposed to maintain the blade support and blade edge in their precise position adjacent the heated surface of the roll by preventing wa1ping of the blade support and twisting of the blade edge under heat radiated from the roll. A particularly successful solution to this problem of blade warping by the heated roll is taught by the United States patent to Richard E. Carvill No. 3,001,296 issued September 26, 1961.

However, in this as well as in other doctor blade support arrangements another very real problem arises in the not uncommon circumstance where a paper machine is located in surroundings where the surface temperature of the doctor blade support is sometimes so low as to cause condensation of water vapor or sweating from the ambient atmosphere. When these circumstances or locations exist, as they may when a cold paper machine is first started after a period of shut-down or where a doctor blade is used in a humid location, such as next to a calender roll operating with a water box, condensate from the atmosphere may collect on the blade support and drip on paper passing through the machine, not only causing water spots on the paper but also sometimes weakening the paper web so that breaks occur, forcing halting of the machine and restarting. This sweating problem is particularly annoying, especially since it occurs under so many different circumstances and at so many difierent locations in various paper making machines. The present invention is directed toward a solution of this problem which is simple, economical and reasonable in that it does not require drastic changes to existing equipment and requires only the addition of certain readily available cornmercial elements or items to a doctor blade support arrangement according to the above noted Carvill patent.

Accordingly, the principal object of the invention is met by providing, in the liquid-filled, hermetically sealed chamber of a hollow doctor blade supporting member,

an elongated immersion heater which is so set or controlled as to maintain the outer surfaces of the doctor blade supporting member at a temperature above the condensation temperature or dew point of the ambient atmosphere surrounding the doctor blade support.

Other objects, advantages and further details of that which is believed to be novel and included in this invention will be clear from the following description and claims, taken with the accompanying drawing in which are illustrated two examples of hollow, liquid-filled doctor blade supports embodying the present invention and incorporating immersion heaters as above generally described.

In the drawings:

FIG. 1 is a perspective view of one side of a doctor blade and its support showing one form of the invention;

FIG. 2 is a vertical transverse sectional view on a larger scale showing the doctor blade and support of FIG. 1 and a portion of a heated roll with which the blade cooperates, and

FIG. 3 is a perspective view like FIG. 1 but showing another form of the invention, parts being broken away to indicate internal details.

In carrying out the objects of this invention, in both embodiments or forms here shown, a heated roll member such as the breast roll 10 is rotatably mounted in a main machine frame 12 in the usual fashion. Brackets 14, also on the machine frame, near the face of the rotating heated roll, provide pivotal mountings for trunnions 16 suitably fixed to and extending outwardly from opposite ends of a doctor blade supporting member 18, here shown as a hollow beam or girder constructed in accordance with the teachings of the above noted patent to Carvill. In the forms shown, this member is composed of an elongated L-shaped or angle beam with side legs or webs 20 and 22 joined together at right angles to each other, an elongated wall 24 bridging the two free margins of the webs to form an elongated chamber 25, the ends of the chamber being closed by suitable end plates 26. These parts are secured to each other as by welding, brazing or in some other suitable fashion, making an hermetically sealed or closed hollow supporting structure :for the blade. In FIG. 2, threaded filler plugs 28 in the wall 24 provide means for introducing into the chamber 25 a heat eX- change liquid, preferably water, which fills the chamber. In FIG. 3, a filler plug 29 in web 20 and a drain plug 31 in web 22 are shown for the same purpose.

When the liquid-filled hermetically sealed supporting beam is suspended between its trunnions, as it would be in use, a doctor blade seat 30 is planed or milled along one margin of the supporting member and a doctor blade 32 is secured thereto as by bolts 34. All this is taught by the above mentioned Carvill patent, and provides a doctor arrangement highly resistant to warping by heat from the roll.

As above noted, under certain circumstances or at certain locations the outer surfaces of the doctor blade supporting member may be at or below the condensation temperature or dew point of the surrounding atmosphere. When this is so, water vapor will condense on the support and drip therefrom, causing the difiiculties mentioned previously. According to the present invention, an immersion heater is mounted along substantially the entire length of the doctor blade supporting member within the hermetically sealed liquid-filled chamber, this heater being immersed and in contact with the liquid filling the chamber. Heat from the element 40 is distributed quickly and evenly in and by the liquid to all parts of the support. Ideally, the elongated heater is a single continuous uninterrutped length and in the form of 'FIG. 1 may consist of a Nichrome resistance wire coil on a ceramic insulating core, enclosed within a waterproof covering of porcelain or similar heat exchanging insulation. The immersion heater 40 of FIG. 3 is a single elongated U-shaped loop of imperforate steam pipe, steam, rather than electrical energy, being used as the heating medium in this embodiment. This heater may use any other suitable medium, such as hot water, if the heater element itself is of a construction adapted for immersion in the liquid-filled chamber and, like the examples using electrical resistance or steam, need not be flexible and in fact a rigid heater is preferred because it is not subject to shifting and can be located and held easily within the hermetically sealed chamber in the best position for most efficient and even distribution of heat therein. Heater carriers such as the U-shaped holding brackets 42 suitably support and hold the heater within the hollow girder and are suitably welded or otherwise secured to the inner wall of the web 22 in the doctor blade supporting member, as shown.

The heater in both forms is thus fixedly supported against the inside of one of the walls of the chamber of the blade support and extends through substantially the entire length of the support. Because steam under pressure is readily available in all modern paper mills, the form of the invention shown in FIG. 3 may be preferred. In this form, a source of steam under pressure, such as from a dryer roll steam pipe line 41, is used to supply eat energy to the heater through a flexible steam hose 43. The temperature of the steam going through the hose to the heater from the steam source is regulated or controlled -by a controlling device such as the pressure reducing valve 45, designed and set to supply suflicient heat to keep the entire doctor blade and outer surfaces of the blade supporting structure always above the condensation temperature or dew point of the surrounding atmosphere. This temperature is predetermined or selected in advance for any particular installation and may be called the control temperature. For example, the normal range of prolonged operating temperature in many paper making machines may be between 180 and 215 degrees Fahrenheit. If valve 45 is set for two pounds of saturated steam it will produce a temperature of about 218 degrees Fahrenheit, and this may be the control temperature for the usual installation.

The steam hose is connected by and through suitable fittings in a wall of the support, shown here as one of the end plates 26 in FIG. 3, to the heater in the hermetically sealed chamber, and the return bend of the heater may also pass through this same wall and be provided with a steam trap 47 with condensate discharge of convenient design. Naturally the connections and fittings must be made so that the liquid in the chamber remains hermetically sealed therein and out of direct contact with the steam in the heater.

If electrical heating is preferred, power for energizing the resistance wire of the heater 40 in FIG. 1 is provided from any suitable source through an ordinary electrical cab-1e 44, and the electrical circuit passes through a temperature controlling device, preferably a thermostatic switch or thermostat 46, located on the outside or inside of the supporting member 18, shown here as on the outer face of the web 22. This control device should be under the influence of and actuated by the outside temperature of the doctor blade support member and it is arranged to close the circuit to provide energy to the heater as long as the outside temperature of the support is below the control temperature mentioned earlier, and to open the circuit to the heater when the outer surface of the support is above this control temperature. Necessary electrical lead wires between the control device or thermostat and the heater element are provided through the web 22 in any desired known fashion, it being understood that the lead wires must not break the water-tight hermetic seal of the liquid-filled chamber and that they are properly insulated.

If desired, and especially when the operating temperature of liquid within the blade support may be high, a

relief valve such as 48 (FIG. 3) may 'be provided for the hollow chamber 25 at one end thereof in either form of the invention. This relief valve permits excess liquid to escape from within the chamber but prevents entry of any fluid into the chamber.

In using apparatus according to the invention, the control temperature is by definition above that at which condensation will occur on the support, and the heater is connected or kept connected to heating power through the control valving or switching device whenever it is likely that the doctor support will fall below the control or condensation temperature, particularly when the paper machine as a whole is shut down for any considerable period or in advance of starting after a shutdown. If moisture has already condensed on the support when the heater is started, it is wiped oif, and operation of the heater thereafter will assist in final evaporation drying of condensate from the support surfaces.

Although the control device could be a hygrometer, operable to supply heat when the temperature drops to a variable control temperature at or slightly above the existing dew point at any given time and operable to discontinue heat when the temperature rises to a selected control temperature only above this variable dew point, in most cases a thermostat or valve control of a relatively simple type is less expensive and works as well for all practical purposes if a predetermined single control temperature setting or selection is made to maintain the doctor blade support approximately at the normal temperature it will assume during prolonged operation of the machine. This is so because usually the normal prolonged machine-operating temperature of the support in any particular installation will be above the dew-point encountered at any time, and condensation therefore can be prevented, without using hygrometric control. Of course, if using a single control temperature setting, when special locations of high humidity are encountered, the control temperature should be so calculated and selected as to keep the doctor blade support at a temperature above the highest dew point expected, even when this is above the otherwise normal machine-operating temperature oi the support.

An incidental advantage obtained by this arrangement resides in the fact that, if the set or selected control temperature is at or near the normal prolonged machine operating temperature, before starting a cold machine the heater may be energized until the doctor blade support reaches this control temperature. This preheating expands the blade support and its associated parts to dimensionally stable normal operating condition before the machine is started to process paper. Fine dimensional adjustment of the blade then may be made with the parts in their preheated condition and later fine or corrective adjustment after starting paper processing is thus substantially reduced. This advantage exists, if the control temperature used approximates or exceeds the machine-operating temperatures, whether or not atmospheres of high humidity are encountered by the doctor blade support.

As will be evident from the foregoing description, certain aspects of this invention are not limited to the particular details set forth as examples, and it is contemplated that various and other modifications and applications of the invention will occur to those skilled in the art. It is therefore intended that the appended claims shall cover such modifications and applications as do not depart from the true spirit and scope of the invention.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

1. In a support for a doctor blade for use in doctoring a heated surface, said support having walls defining an elongated hollow chamber occupying the entire interior of said support and providing support for said doctor blade between its ends,

a mass of liquid substantially completely filling said chamber thereby providing a substantially complete- 1y liquid-filled chamber occupying the entire interior of the doctor blade support and means sealing said liquid mass in the chamber,

that improvement for maintaining the entire said support at a temperature above a control temperature comprising an elongated imperforate immersion heater element mounted within said sealed chamber of said support, said heater element extending substantially the length of said chamber in heat exchanging contact with said liquid mass therein,

a source of energy for said heater outside of said support and a control device connecting said energy source to said heat exchanging contact with said liquid mass therechamber adapted for energizing said circuit to said heater when the outside surface of said support is below a control temperature at least as high as the dew point of the surrounding atmosphere and for interrupting said circuit to said heater when the temperature of the outside surface of said support is above said control temperature,

whereby said heater biases the temperature of the liquid in said chamber and the entire outside surface of said support toward a temperature above that at which water vapor will condense on said support from the surrounding atmosphere.

5. A doctor arrangement including a doctor blade for use in doctoring a heated roll which comprises heater to maintain the temperature of the outer suran elongated hollow liquid-filled hermetically sealed face of said support above said control temperature, girder having said control temperature being above that at which side and end walls defining a completely liquid-filled water vapor will condense on the outer surface of chamber occupying the entire interior of said girder, said support from the surrounding atmosphere. means adjacent each end for pivotally supporting said 2. The improvement of claim 1 in which said control girder adjacent the face of said roll, temperature is approximately at the normal temperature means along a margin of said girder for mounting said said doctor blade support will assume during prolonged doctor blade with its operative edge extending latuse thereof. erally from said girder toward the face of said roll, 3. The improvement of claim 1 in which the walls of said girder supporting said doctor blade said source of energy is a supply of steam under presin operating position against substantial sagging sure, under the influence of gravity on said liquid-filled said heater is an elongated imperforate steam pipe and girder, said control device is a valve connecting said supply an elongated electrical heater inside said hollow sealed of steam to said steam pipe heater, girder chamber extending substantially the length of to maintain the temperature of the outer surface of said chamber and immersed in the liquid filling said said support above said control temperature. chamber and 4. In a support for a doctor blade for use in doctoring a thermostatic switch mounted on said chamber for a heated surface, said support having controlling the operation of said heater inside the walls defining a single elongated hollow chamber ocgirder in accordance with the temperature outside cupying the entire interior of said support and prosaid girder to maintain the entire outer surface of viding support for said doctor blade between its the girder at a temperature above the dew point ends, of the surrounding atmosphere. a mass of liquid substantially completely filling said chamber thereby providing a substantially completely References Cited y the Examine! liquid-filled chamber occupying the entire interior UNITED STATES PATENTS the 9 d P 9 2,050,254 8/1936 Barnsteiner 34 port comprising g g 2,376,502 5/1951 Overton 15-25651 an elongated electrical immersion heater mounted with- 3134126 5/1964 Phlmps 15256'51 in said sealed chamber of said support, said heater FOREIGN PATENTS extending substantially the length of said chamber in 2,141,462 12/1938 Great Britain.

CHARLES A. WILLMUTH, Primary Examiner.

an electrical circuit to said heater and temperature control means in said circuit on said WALTER SCHEEL Examiner 

1. IN A SUPPORT FOR A DOCTOR BLADE FOR USE IN DOCTORING A HEATED SURFACE, SAID SUPPORT HAVING WALLS DEFINING AN ELONGATED HOLLOW CHAMBER OCCUPYING THE ENTIRE INTERIOR OF SAID SUPPORT AND PROVIDING SUPPORT FOR SAID DOCTOR BLADE BETWEEN ITS ENDS, A MASS OF LIQUID SUBSTANTIALLY COMPLETELY FILLING SAID CHAMBER THEREBY PROVIDING A SUBSTANTIALLY COMPLETELY LIQUID-FILLED CHAMBER OCCUPYING THE ENTIRE INTERIOR OF THE DOCTOR BLADE SUPPORT AND MEANS SEALING SAID LIQUID MASS IN THE CHAMBER, THAT IMPROVEMENT FOR MAINTAINING THE ENTIRE SAID SUPPORT AT A TEMPERATURE ABOVE A CONTROL TEMPERATURE COMPRISING AN ELONGATED IMPERFORATE IMMERSION HEATER ELEMENT MOUNTED WITHIN SAID SEALED CHAMBER OF SAID SUPPORT, 